Decision guide
What building private RAG in-house commits you to, what buying a platform commits you to, and how to judge both against the same requirements.
Definition
Build versus buy is a decision about which capabilities and lifecycle responsibilities the organisation should own.
The capability is strategically differentiating, hard requirements are not met by available products and the organisation has durable product, security, evaluation and operations ownership.
The implemented product layers meet your hard requirements and the deployment, support and commercial boundary is acceptable. Internal teams then spend their time on domain configuration and adoption.
A model API and a vector store are the visible part. Everything around them is the work, and it does not stop after launch.
Use the same documents, expected answers, failure cases, permission tests and reviewer rubric against the internal prototype and shortlisted platforms.
Document hard constraints, weighted preferences, dependency risk, portability and the conditions that would trigger a revisit. A hybrid approach may also fit.
These are the usual patterns, not fixed rules. A contract, an architecture or a team's capability can move any row.
| Decision factor | Internal build | Product platform |
|---|---|---|
| Product differentiation | Maximum design freedom; the organisation must decide and maintain every product layer. | Constrained by implemented product screens and roadmap; domain configuration may still differentiate the workflow. |
| Evidence and evaluation | The organisation designs, operates and maintains the evaluation harness and release gates. | The vendor should expose evaluation surfaces and evidence; the buyer still validates on its own workflow. |
| Security and operations | Identity, isolation, monitoring, incident response, upgrades and support are internal responsibilities. | Responsibilities are shared and must be stated for the selected managed or self-hosted deployment. |
| Integration | Any integration can be designed, but every connector lifecycle remains internal work. | Use implemented native or protocol paths; unverified systems remain scoped requirements. |
| Exit and portability | Code ownership may improve control while creating dependency on internal maintainers and chosen services. | Contract, export formats, data model, configuration and provider dependencies need explicit review. |
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No. Compare full lifecycle cost and opportunity cost using the organisation's actual requirements and ownership model.
Yes. A platform can supply common product layers while internal teams build differentiated workflows, integrations or evaluation around it. Review dependency and support boundaries.
Use the same constraints, corpus, failure cases and operating assumptions for an internal prototype and Marella AI.